1
An Environment Friendly Autonomous ATV Practical Mechatronic Project R. Sell, M. Tamre Department of Mechatronics, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia; Phone: +3726203201, Fax: +3726203203, e-mail:
[email protected] Department of Mechatronics, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia; Phone: +3726203202, Fax: +3726203203, e-mail:
[email protected]
Abstract — The project deals with a practical mechatronics project involving final year bachelor students. The aim of this project is to refine the student’s teamwork, project management skills together with true mechatronics application. The application is ATV based mid-size autonomous mobile robot with the special functionality. An important focus of the project is also the environment friendly energy solutions. Index Term - mobile robot, mechatronics project, project based learning.
Figure 1 Outlook of result in 2006 & 2007 I.
INTRODUCTION
The mobile robotics market demand is drastically increased during last years. Robotic markets are set to grow quickly and become large economic sectors in their own right as well as providing the means for both manufacturing and service industries to become more effective [1]. Sales for domestic robots (vacuum cleaning, lawn mowing, window cleaning and other types) is expected to reach over million units, while sales for toy and entertainment robots will exceed more than million units [2]. On the frame of these trends the mechatronics project of mobile robotics was established on the 2006 at department of Mechatronics in Tallinn University of Technology. The idea was to develop practical mid-size robotic application for the use of agriculture or urban areas. The application development is a mechatronics project for third year bachelors before the final work. Project lasts 2 month. It was started at last year when we acquired the base platform from standard mid-size ATV (All Terrain Vehicle) and removed the compulsion engine and drive mechanism. The result of 2006 teamwork was completely developed electrical drive and turning system, computer control software and sensor system. This year 2 month project continued the work and rebuild almost all system with added functionality. Although the result of last year teamwork worked quite well, the students of this year decided to rebuild the mechanics due the weak engines and transmission mechanisms. In control side the selected data exchange protocol wasn’t good enough to transfer the increased amount of data. The figure 1 shows the outlook of 2006 and 2007 results.
The mechatronics project course was divided into four groups: • Mechanics • Energy • Control • Functionality Every group has approximately 8 persons, project leader and integration manager. Groups had following tasks: Mechanics team The mechanics team had to develop and reengineer the main drive mechanism and turn mechanism. Both had to be powered by the electrical engines. In addition they had to develop the main controllers for engines. The challenge was also to rebuild the last year design and develop completely new design solution. Big freedom for this task was given and the team was enabled to develop as novel design as they can. Energy team The energy team was responsible for all cabling and main relay box. They had to develop professional cabling solution with switches, fuses and emergency stop system. Another main task was to develop an environment friendly power system and study different possibilities for that. Control team: The control team was responsible for control system, which when ready, should allow controlling the robot using PC, RC remote and joystick. They also had to develop interface and choose appropriate communications protocol. The remote
2 control has to perform on the basis of radio control using a modem. Functionality team The functional team was given a responsibility to handle all problems relating to functionality. That meant following tasks: 1. Driving by coordinates received from GPS 2. Avoiding obstacles using sensors 3. Radar or a laser sensor to effectively avoid and identify obstacles in front. 4. Handling signals received from sensors II. PROJECT SOLUTION The goal of this project was to build a mobile robot which would have the following functional capabilities: • An autonomous regime means that it could travel from one point to another by using GPS, whereas it should manage avoiding obstacles by using sonars and laser scanner; • RC/PDA control, where the ATV is controlled by using the radio controlled (RC) remote and PDA as a sensor feedback. This is a short-range operation option; • PC control, where the computer (laptop) control interface with external joystick is used. The communication is over the WLAN, WIMAX or radio modem, enabling full functionality in long-range control. The control solution has a special Graphical User Interface (GUI) with debugging options; • Video feedback.
Functionality team experienced several difficulties during the development. Getting the GPS to function properly was not a hard task. The device sent out a string, which included also the coordinates, so the only problem was to cut out the necessary part. However the main trouble was to get the ultra sonic sensors work properly. The data they gave was inconsistent and the sensors themselves crashed frequently. Finally they achieved non-crashing SRF08 sonar. The achievement was even more exceptional because both of our programmers did it almost simultaneously, though separately. On the end the team were faced with numerous small details. This work includes: summaries of weekly reports, working principles of sonar and digital compass, program codes (written in C++) and an explanation of how the autonomous algorithm works. Analogous problems and working rytms was also with other teams. The user interface of robot was developed by the control team. They had to develop 2 independent control methods. The PC control had to have user interface with the control buttons and sensor feedback. In addition the interface has the GPS coordinate insert form. The figure 3 shows two tabs of developed interface.
Target
2 Desired direction 2.3 2
1
3
Actual direction
Start
Figure 2 The GPS navigation On the figure 2 the GPS navigation idea is illustrated. Every GPS cycle (around 1 sec) the distance between robot and target is calculated. If the value is below the set value (in testing 5 m) then the robot is gained the particular location point and will either stop or move to the next location point. Robot will move straight forward calculating its moving direction and adjusting itself according that. The 5 meter distance was selected because the robot has the turning radius and if this is bigger than target distance error then the robot might just start to cycle over the location point.
Figure 3 Graphical User Interface for PC The secondary control system is a short-range control and was realized with RC remote from car model. The figure 4 shows the selected solution.
3 they acquired good practice in project management and teamwork where experience shows that synergistic teamwork is often quite difficult to reach. An important experience is also an integration of the results between the development teams, which is also very difficult to archive. However the course is almost always claimed as much more interesting and useful than conventional ones. Nevertheless this sets high demands for the supervisors and need much more work to deal with all problems during the course. The full report is available in our public website mechatronic.ttu.ee [4]. Figure 4 RC remote control transmitter & receiver PWM1 - Steering (PIN C7) PWM2 - Throttle (PIN C6) PWM3 - Auxiliary The communication protocol was chosen after the comparative analyze of different available protocols. Selected data exchange protocol was ModBus [3] due the proven error handling and simple architecture. The control architecture is shown on figure 5.
Figure 5 Control and communication diagram The sensor system of the solution exploits mainly ultra sonic sonars SRF08 as a side and back sensing devices. In front, a long-range laser scanner Sick LMS291 is used. For this year the project is ended and next year new teams will continue the development and practical application is hopefully archived. III. CONCLUSION This paper presents a practical mechatronics project and the achievements of student teams. The feedback of this kind of mechatronics courses is very excellent and students learn much more compared with conventional lectures. They spend working time usually more than expected by the curriculum and stay in laboratory much often than required. In addition
REFERENCES [1] European Robotics Platform, [WWW] http://www.robotics-platform.eu.com/, 2007-03-01. [2] Worldwide Market, International Robotic Association, [WWW], http://www.robotinvestments.com/RI_worldwide_market. htm, 2007-02-20. [3] ModBus [WWW] http://www.modbus.org, 2007-03-01. [4] Mechatronics project MHK0020 [WWW], http://mechatronics.ttu.ee/.
